$S =\{(x_i, y_i)\}^n_{i=1}$ the dataset, with $x_i \in X$ and $y_i \in Y$. $T =\{t_1, t_2, \dots, t_d\}$ the random forest of $d$ trees, such that $t_j : X \rightarrow Y$.
\section{Orthogonal Matching Pursuit (OMP)}
$y \in\mathbb{R}^n$ a signal. $D \in\mathbb{R}^{n \times d}$ a dictionnary with $d_j \in\mathbb{R^n}$. Goal: find $w \in\mathbb{R}^d$, such that $y = Dw$ and $||w||_0 < k$. $\text{span}(\{v_1, \dots, v_n\})\{u : u =\sum^n_{i=1}\alpha_i v_i \ | \ \alpha_i \in\mathbb{R}\}$.